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Researchers study effects of social stress on live-birth sex ratios Professor, assistant exc male fetuses are miscar Susanne Bust Milwaukee Journal Sentinel MILWAUKEE — For years, researchers have observed that when women are faced with periods of economic or environmental distress, the number of male babies bom, in comparison to females, declines. But why this phenomenon occurs is not known. Now, some researchers think they have figured it out — and they say it has more to do with the promise of the future than the stressful realities of the day. Ralph Catalano, a professor of public health at the University of California — Berkeley and an economist by training, has long been interested in the way sex ratios seem to coincide with current events. In 2003, he compared male live-birth rates in East and West German hospitals from 1946 to 1999. He discovered that while the sex ratios remained pretty stable for most of the 45 years, in 1991, there was a sudden drop in the number of East German boys born. The sex ratio is the number of males per 100 females. Under normal circumstances the sex ratio should be just above or just below 100. According to Catalano, the East German dip was the probable result of the country’s 1991 economic collapse. West Germany, which didn’t experience the collapse, didn’t show a corresponding anomaly. I” mine belief that more ried in times of trouble In 2005, he made a similar observation when he looked at data collected in California after the terrorist attacks of Sept. 11, 2001. The birth cohort, born four to five months after the Researchers have long known that males tend to have lower life expec tancies than fe males as fetuses, embryos, children, and adults. attacks, had fewer males. This observation, he said, corresponds with what biologists know about stress, pregnancy and sex ratios. Researchers have long known that males tend to have lower life expectancies than females as fetuses, embryos, children and adults. Indeed, it’s not until people reach their 90s that men start outliving females, Catalano said. It’s also been shown that more male fetuses and embryos are miscarried than females. This phenomenon becomes particularly apparent after six weeks of gestation, but the biological mechanisms behind it are not known. Some speculate that males are extremely sensitive to stress in the mother’s body. According to this theory, if a woman is producing and circulating high concentrations of stress hormones, called glucocorticoids, the male fetus might react badly, and possibly die. If that theory is true, then the observation that the male sex ratio was lower in the birth cohort four or five months after the Sept. 11 terrorist attacks would match the timing. But why a woman’s body might spontaneously reject a male fetus or embryo has been hotly debated for years. And although two reigning hypotheses fuel the fight, until now no one had put them to the test using human population data, Catalano said. The first hypothesis, called the “culled cohort,” argues that women’s bodies will miscarry weak male fetuses and embryos during stressful times because weak sons will produce fewer offspring than weak daughters. Therefore, miscarrying a weak male should allow the mother to begin a new pregnancy with the possibility of yielding a daughter or a more robust son. The hypothesis assumes that during stressful periods the criteria for a weak male and an acceptable son will change. In a healthy environment, a slightly weak male may not be so badly off. However, that same male in a stressful or harsh environment might not survive. Therefore, the hypothesis states, during stressful times the mother’s body will miscarry males that in happier times might be deemed acceptable. The second hypothesis, called the “damaged cohort,” argues that fetuses simply die as the byproduct of a mother’s internal stress response. As a result of the mother’s internal response, every exposed fetus will become weaker. The hypothesis suggests that both weak males and females will be miscarried, but presumably more males will be affected because they are generally weaker. Catalano wanted to determine which hypothesis best explained the demographic data. Do these deaths have a selective value, he wondered, or are they just the result of women’s biology gone wrong? If the “culled cohort” hypothesis was correct, he said, one would expect the sex ratios of live births to fall as a result of a higher number of miscarried male fetuses, and thus there would be fewer males born alive because more males died in utero. One would also expect that males born in cohorts with relatively low sex ratios would survive longer, on average, than those born in other cohorts. That’s because the shift in criterion — what constitutes a normal vs. weak male — should have culled all males except for the strongest and healthiest. On the other hand, if the “damaged cohort” hypothesis explains the dips, he said, then one would expect to see just the opposite: The survival of males born in these cohorts should be lower than males born in other cohorts. As the mother’s body experiences stress, he explained, her fetus becomes damaged and weakened by it. Every child 1 born during such a time, therefore, wilj be weaker than children born in more benign periods. Catalano and his co author Tim Bruckner, also of University of California — Berkeley, looked at data collected on Swedish men from 1751 to 1912. They chose 1912 as the end date because most men *r born during that year are now dead, enabling the researchers to look at the men’s lifespans. Figuring that the live birth sex ratio should predict survivability, and therefore lifespan, the researchers analyzed the data and discovered that men bom in low-sex-ratio birth cohorts Jived longer than other men. YTfflflD • connnueo FRO(Tl 6 on YTMND for several months when it surfaced on eBaumsworld.com. When the creator of the animation was reached, it was revealed that he never gave permission for eBaumsworld to host the Tile. • Outraged, the YTMND community took action. While many of their tactics were illegal, such as death threats and hacker attacks, the Lohan 'animation was quickly removed from eBaumsworld. With the war over, YTMND hopes its popularity will continue to rise and that its ongoing fads will grant the site a long and prosperous Comments on this story? E-mail gamecockfeatures@gwm. sc. edu SOLUTIONS Suggestions for The Mix? E-mail gamecockfeatures@gujm.sc.edu ---1 Science ! 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